October 2012

​Canine blood smear

A labrador mixed breed dog was diagnosed with ehrlichiosis based on serology but did not respond to doxycycline treatment. Examination of blood smears revealed these organisms. What parasite is this?

What is your diagnosis? Scroll down to see the answer...

Answer:​This is Hepatozoon americanum, the agent of American canine hepatozoonosis. Dogs become infected when they ingest an infected tick containing sporulated oocysts or a transport host, such as a rabbit or rodent, harboring cystozoites. Dogs with hepatozoonosis require aggressive antiprotozoal therapy and do not respond to doxycycline treatment.